Hard metal body with hardness gradient, such as punching tools

ABSTRACT

The invention relates to a method for the production of a body made of hard metal, consisting of a hard compound A and a binder B, wherein pulverulent A and B, or an optionally precompacted article that contains A and B, are introduced into a container and the material containing A and B is compacted in order to increase the relative density (RD) to a value that is higher than 70% of the theoretical maximum density (TMD). The invention further relates to a body of hard metal comprising a hard compound A and a binder B, the mass ratio of A:B gradually changing over a cross-section of the body in order to impart to said body different mechanical properties in one zone Za or to one end (T) and hardness in one zone Zb or to another end (H). The invention also relates to the use of dynamic compaction techniques for the production of such bodies.

[0001] The invention relates to a body made of gradual hard metal, suchas punching tools, and a method for the production thereof. The use ofstatic and dynamic compaction techniques known per se for the productionof new bodies made of hard metal, such as tools having a hard first endand a tough second end, for example cutting and shaping tools such aspunching tools, plays an essential role according to the invention. Anexplanation of the terms used in this description and claims and of thetechniques employed according to the present invention is first givenbelow, before discussing the invention in detail.

[0002] Bodies made of hard metal

[0003] Bodies made of hard metal are understood to be products whichcontain a hard compound such as a metal carbide and metallic binder andwhich have been subjected to sintering or hot isostatic pressing. Theirrelatively high carbide content makes the hard metal stiff, hard andresistant to wear. The binder imparts the necessary toughness andstrength to the whole.

[0004] In the present description and claims the hard compound isindicated by A and the metallic binder by B.

[0005] The hard compounds A are, for example, carbides, borides,nitrides and diamond.

[0006] The hard compounds A have the following characteristics: highhardness, low toughness, high compressive strength, low tensile strengthand a high melting point. In addition they are not ferromagnetic or veryslightly ferromagnetic. Tungsten carbide is the most widely used hardmetallic compound in hard metal products.

[0007] The tough compounds B are, for example, metals such as Co, Cr,Ni, Fe (stainless steel) and alloys thereof.

[0008] A great deal of information on hard metal products and themethods for the production thereof, including sintering and hotisostatic pressing, is to be found in the general technical literatureand in the patent literature. For a general review of “cementedcarbides” reference can be made to the ASM Metals Handbook, 9^(th)Edition, Vol. 16, “Machining”, pp 71-83, published in 1989. The contentsof this publication must be regarded as incorporated here.

[0009] Reference can also be made to the book entitled Cemented TungstenCarbides, Production, Properties and Testing, 1998, by Gopal S.Upadhyaya, published by Noyes Publications, U.S.A., for the productionand properties of and test methods for hard metal products based ontungsten carbide. In this context reference is made in particular to theinformation on sintering and hot isostatic pressing (HIP) includingsinter HIP. The relevant text on pp 110-130 of this publication byUpadhyaya must be regarded as incorporated here.

[0010] Static and dynamic compaction techniques

[0011] Static and dynamic compaction techniques are known per se for thecompaction of pulverulent materials.

[0012] Static compaction techniques which can be used in the context ofthe present invention are therefore generally known and appear torequire no further explanation. For a review of static compactiontechniques which (can) play a role in the context of the presentinvention reference can be made to J. S. Reeds, Principles of CeramicProcessing, 2^(nd) ed, J. Wiley & Sons, New York (1995).

[0013] For dynamic compaction techniques which (can) play a role in thecontext of the present invention reference can be made to thepublication entitled “The Dynamic Compaction of Powdered Materials” byS. Clyens and W. Johnson in Materials Science and Engineering, 30(1977), 121-139. In this publication four main areas in which powdercompaction processes are used are indicated: the powder metallurgy,fuels, ceramics and pharmaceutical industries. The following is statedwith regard to these industries: “Powder metallurgy fabricationtechniques have been developed for three principal reasons. Firstly,because for some components and materials established methods of formingare not suitable, e.g. refractory metals have long been fabricated bypowder metallurgy because of the difficulties encountered in melting andcasting. Secondly, in some cases powder metallurgy processes are moreeconomical; many iron-base alloys are fabricated from powders intofinished components because the savings in materials and machining makeit worthwhile. Thirdly, the greater control of both grain size andcomponent distribution afforded by the processes often results in a morehomogeneous metallurgical structure.

[0014] For many years the ceramic industry has employed compactiontechniques to form dry- or slightly moist ceramic powders into a widerange of products. The dry-pressing technique has two main advantages;unlike the wet-forming methods, dry pressing may be fully automated withhigh rates of production and one operator may take charge of severalpresses. Also, as the powder is pressed dry, the expense of filterpressing and drying is avoided, so that dimensional tolerances to betterthan 1% in the fired product may be achieved.

[0015] The pharmaceutical industry employs powder compaction processesto form medicinal powders into tablets. Tabletting has been used mainlyas a convenient and simple form of dosage and there are now fewcountries in which tablets are not manufactured.

[0016] In the fuel industries many processes lead to the production ofpowdered fuels which cannot be handled conveniently or re-used. Suchpowders have often been disposed of as waste representing an economicloss to industry and, in some instances, a major cause of pollution.Compaction processes have been used to form these powders intobriquettes which may be handled easily and used again.”

[0017] It is pointed out that the above information does not relate torelatively substantial compaction. The compaction technique that is usedin the ceramics industry relates, for example, to the pre-pressing ofceramic powders before they are sintered, so that the “dimensionaltolerance is better than 1%.” What is concerned here is, in fact, acompaction that is used as possible (non-mandatory) precompaction in themethod according to the invention, as is described in more detailfurther below.

[0018] Following the introductory remarks on the static compactionmethods that were conventional in 1977, the publication by Clyens et al.gives consideration to the dynamic compaction methods. The following isstated with regard to the difference compared with the compactionmethods customary up to that time: “These methods differ from the moreconventional consolidation techniques in respect of the compactingpressure and the speed or rate of compaction used. There is now someevidence to suggest that increasing the rate of compaction results in amore uniform density distribution, improved green strength, and in thecase of die compaction lower compact ejection forces.” The following isstated in the sentence that runs from page 121 to page 122: “In thepowder metallurgy and ceramic industries efforts have concentratedmainly upon developing methods capable of producing high-densitycomponents of complex shape or large, semi-finished articles, whereas,in the pharmaceutical and fuel industry, interest has concentrated uponincreasing production rates.”

[0019] The compaction referred to in the abovementioned literature ofcourse results in a reduction in the porosity. This means that the porevolume is reduced and thus that the density increases. In the presentcontext—including that of the invention discussed further below—thedensity is not cited as an absolute value (in g/cm³) but as relativedensity (RD) with respect to the density of the solid without pores, orthe theoretical maximum density (TMD) of the substance. It is clear thatwith the known compaction discussed above relatively little compactiontakes place in the field of hard metal production, the RD of thematerials concerned never being raised to a value that is aboveapproximately 65% TMD, which will be immediately apparent to thoseskilled in the art.

[0020] For the dynamic compaction techniques and the mechanisms on whichthese are based, reference is made to the cited publication by Clyens etal., the contents of which must be regarded as incorporated here.

[0021] The problem on which the present invention is based

[0022] As indicated in the first paragraph of this description, theinvention relates to bodies made of gradual hard metal and theproduction thereof. The problem on which the present invention is basedis explained with reference to punching tools, but comparable problemsare experienced with a wide variety of tools which are produced fromhard metal and which (have to) possess different mechanical propertiesin different locations.

[0023] Punching tools must be hard (wear-resistant) at the punching edgeand be impact-resistant (tough) at the recoil edge. To date it has notbeen possible to combine these properties within one material andpunching tools are therefore in general made up of two materials. Therecoil edge is generally made of fast steel (a type of wear-resistantsteel), whilst the punching edge consists of hard metal (tungstencarbide with cobalt, WC/Co). These materials are mechanically joined toone another. As a result play develops in the joint during use of thetool, which leads to a reduction in the product quality. This limits thepunching time of the punching tool (such as punching stamps), as aresult of which this tool has to be replaced prematurely, which has theeffect of increasing costs and as a result of which the productionprocess has to be interrupted many times. It would therefore bedesirable to have punching tools that are constructed entirely of hardmetal, but in which there is nevertheless an impact-resistant (tough)edge and a wear-resistant (hard) punching edge as a result of thegradual change in the composition. With regard to this problem referenceis made, for example, to U.S. Pat. Nos. 4,820,492 and 5,543,235.

[0024] For instance, it is described in the preamble of U.S. Pat. No.4,820,482 that diffusion of the binder phase takes place duringsintering of bodies made of hard metal, which leads to sintered bodiescontaining a virtually uniform binder phase. The technique with whichstarting materials with different particle sizes are used or with whichthe hard metal body is subdivided into zones of different particle sizesis also discussed. These techniques also fail to produce bodies with, onthe one hand, impact-resistant locations and, on the other hand,wear-resistant locations in a controlled manner. This patent gives asolution to this problem by the use of “carburizing” the sintered bodyto such an extent that the so-called eta phase can be completely removedduring this operation. With this technique a body is produced that hastwo zones: a core with a relatively high binder content and a surfacezone with a relatively low binder content (and possibly small amounts offree graphite). It is true that a body which has a core that hasdifferent properties to the surface can be obtained with this technique,but bodies which have an impact-resistant edge and a hard punching edge,in which there is a gradual transition of the binder content, cannot beproduced according to this technique.

[0025] The abovementioned U.S. Pat. No. 5,543,235, in which “multiplegrade” products of hard metal and a method for the production thereofare described, is of more recent date (1996). It is also reported in thepreamble of this patent (column 1, lines 56-64) that “cemented carbidearticles are invariably fabricated having a substantially uniformcomposition and microstructure . . . and substantially uniformproperties throughout the volume of the article. Many such substantiallyhomogeneous compositions exist in the prior art.” According to this U.S.patent the starting materials for the hard metal body are introducedinto a mould that can be subdivided into various compartments, it beingpossible to remove the partitions between these compartments. Thecompartments are filled with different mixtures, after which thepartitions are removed and the powder is compressed to give a “singlecompact” of the desired shape. Sintering is then carried out.

[0026] The problem is also discussed in the recent (1998) abovementionedbook entitled Cemented Tungsten Carbides by G. Upadhyaya, in particularpp. 365/366, where the following is stated under “Functionally GradedCemented Carbides”: “Composition gradient cemented carbide tools areexpected to offer a number of advantages for specific engineeringapplications. For example, a tough bulk and a hard surface would beinteresting in the case of cutting picks used in the mining industry,which are subjected to shocks.

[0027] The first attempt to study a model of such a type of structurewas done by Cooper et al. in order to explain the migration of cobaltfrom the coarse grained to fine grained layers of a hard metalcomposite. The driving force for migration was the higher capillaryforces existing in the fine grained layer during liquid phase sintering.

[0028] Coling et al. investigated multilayer graded structures in WC-Cocemented carbides with cobalt content varying from 10-30 wt. % from oneside of the structure to the other, prepared by solid state or liquidphase sintering routes. In the case of solid state sintering, the gradedstructure remained after sintering, as there was no risk ofhomogenization during such sintering. In the case of liquid phasesintering, the sintering time had to be much shorter becausedensification occurred much faster with the liquid phase. This requiredprecise control of sintering time, which had to be as short as possiblein order to avoid homogenization of the structure. In the former case,to obtain dense material, post-sintering treatment became necessary.”

[0029] According to the invention the problem of undesired masstransport, leading to homogenisation, is solved in that a method isprovided which makes it possible to produce bodies that consistvirtually completely of hard metal with a minor amount of binder, inwhich the composition of A and B has a gradual transition.

[0030] The invention therefore relates to a method for the production ofa body made of hard metal, consisting of a hard compound A and a binderB, wherein

[0031] chosen amounts of pulverulent A and B, or of an optionallyprecompacted article that contains A and B in chosen amounts, areintroduced into a container and

[0032] the material containing A and B is subjected to compaction in oneor more steps in order to increase the relative density (RD) to a valuethat is higher than 70% of the theoretical maximum density (TMD) withthe formation of a body made of hard metal, in which

[0033] on the one hand at least one zone (Za) containing a relativelylarge amount of B and, on the other hand, at least one zone (Zb)containing a relatively small amount of B are present and

[0034] the amount of B gradually decreases from at least one zone Za toat least one zone Zb,

[0035] after which said body is optionally subjected to sintering, hotisostatic pressing (HIP) or sinter HIP.

[0036] Where mention is made in the present description and claims ofcompaction, this does not refer to the consolidation that takes placeduring a temperature treatment such as sintering, HIP or sinter HIP.

[0037] The method according to the invention makes it possible toimmobilise B with respect to A in a desired and controlled manner. Theterm immobilisation of B with respect to A is used to indicate thatcomplete mass transport of B does not take place, or there is virtuallyno mass transport of B, during sintering or hot isostatic pressing(HIP). The invention is based on the insight that this desiredimmobilisation of B, that is to say incomplete mass transport duringsintering or HIP, can be achieved by reducing the pore volume of thepulverulent starting material A and B to a suitable value. Thisreduction in the pore volume goes further than the precompaction knownfrom the prior art, which precedes sintering or HIP of precursors. Ashas already been stated above, the precompaction according to the priorart is of the order of magnitude of at most 65% TMD.

[0038] In order to obtain the desired immobilisation of B duringsintering or HIP it is preferable to achieve a compaction of thestarting material in excess of 80% TMD, in particular in excess of 90%TMD.

[0039] The greater the compaction the less is the transport of B duringsintering or HIP. The transport or immobilisation of binder B can becontrolled via the T,t effect. High compaction (even up to 100% TMD)ensures a very appreciable or even complete immobilisation of B withrespect to A according to the invention if the compacted product issubjected to sintering or HIP. Thus, too long a sintering time and/ortoo high a sintering temperature will still (ultimately) lead to a hardmetal with a homogeneous composition. On the other hand, too short asintering time and/or too low a temperature will result in inadequatediffusion of B, as a result of which the (too) steep B gradient willcontinue to exist in the end product.

[0040] The problem with conventional hard metal production is that theT,t combination that is required for removal of the porosity (a primaryrequirement for strong products) already produces homogenisation of thebinder B. The compaction according to the invention makes it possible tosinter gradual hard metal to close all pores before homogenisation takesplace to a substantial extent or completely.

[0041] No special requirements with regard to the particle sizes of Aand B are imposed with the method according to the invention. In thiscontext reference can be made to the values for the particle sizes asare used in conventional hard metal production.

[0042] The compaction according to the invention can be carried out inone step or in various steps. It is often effective to subject thepowder of A and B, which is introduced into a container in a controlledmanner, to a precompaction, as a result of which the subsequent finalcompaction step or steps are more effective. Therefore, according to apreferred embodiment, the invention relates to a method as describedabove, wherein the compaction is carried out in two steps:

[0043] (a) a first compaction (precompaction) to increase the RD to avalue of at most 70% TMD;

[0044] (b) a second compaction in which the RD of the precompactedpowder or article from step a) is further increased to a value above 70%TMD, preferably above 80% TMD, in particular to above 90% TMD.

[0045] The method according to the invention makes it possible formechanical joins, which are frequently used in tools such as punchingtools, to be eliminated because, according to the invention, tools canbe produced which are made up entirely of hard metal (with a varyingpercentage of binder). Because the composition of A and B graduallychanges there is still an impact-resistant (tough) edge and awear-resistant (hard) punching edge. Therefore, the invention alsorelates to a method as described above wherein different mixtures of Aand B are introduced into two or more zones of the container, the massratios of A:B in the two or more zones having different values.

[0046] For, for example, the production of punching tools, according tothe invention a method is employed in which the container has anelongated shape and the container is filled with different mixtures of Aand B in such a way that the quantity of binder at the one end of theshape H is lower than that at the other end of the shape T. Possibleembodiments are explained in more detail further below in thisdescription with reference to drawings.

[0047] Thus, with the method according to the invention, in general usewill be made of varying amounts of A and B, the amount of B at the hardend of course being low and the amount of B at the tough end beingrelatively high. In this context it is preferable that the amount of Bat end H of the shape is at least 1% (m/m) and the amount of B at theend T of the shape is at most 50% (m/m), the amounts being based on themass of the total mixture. The invention makes it possible to allow theamount by mass of B to increase gradually from end H to end T. Wheremention is made in this description of “end H” and “end T” this is alsointended to refer to zone Zb and zone Za, respectively. By the choice ofthe “geometry” of the starting materials (sequence) it is possible todefine articles having a wide variety of conceivable zones of hard andtough regions, including “within” the articles.

[0048] Starting materials A and B that can be used are the known hardcompounds on the one hand and the known metallic binders on the other.In this context reference is made to the literature cited in thepreamble to this description. Preferably, A is chosen from the groupconsisting of diamond or carbides such as SiC, WC, TiC, TaC, NbC, ZrC,HfC, Cr₃C₂, Mo₂C, nitrides such as TiN, HfN and BN and borides such asTiB₂ and ZrB₂, in particular tungsten carbide, and B is chosen from thegroup consisting of the metals Co, Cr, Ni, Fe (for example stainlesssteel) and alloys thereof, in particular cobalt.

[0049] The compaction according to the invention is preferably carriedout at a temperature at which no mass transport of the one componentinto the other component takes place, that is to say diffusion of both Band A is avoided. This means that no special measures have to be takenwith regard to the temperature. Compaction is preferably carried out atambient temperature. This contributes to simple implementation of themethod according to the invention.

[0050] It will be clear that the reduction in the pore volume ofpulverulent A and B constitutes the core of the present invention. Thisreduction in pore volume can be achieved in accordance with methodsknown per se. With the method according to the invention use isgenerally made of static or dynamic compaction techniques, preferably(iso)dynamic compaction techniques, such as pneumomechanical uniaxialcompaction, ballistic compaction, explosive compaction, including shockcompaction, and magnetic compaction, for the compaction. For thecompaction techniques reference is made to the information andliterature given in the preamble to this description.

[0051] The invention also relates to hard metal bodies which areobtainable according to the abovementioned methods according to theinvention, as well as bodies of hard metal comprising a hard compound Aand a binder B, the mass ratio of A:B changing over a cross-section ofthe body in order to impart to said body different mechanical propertiessuch as, on the one hand, toughness in at least one zone Za or at atleast one end (T) and, on the other hand, hardness in at least one zoneZb or at at least one other end (H), the change in the ratio of A:Bbeing gradual. The invention also relates to the use of dynamiccompaction techniques such as pneumomechanical uniaxial compaction,ballistic compaction, explosive compaction including shock compactionand magnetic compaction for the production of one-piece bodies made ofhard metal having at least one hard zone (Zb) or hard end (H) and atleast one tough zone (Za) or tough end (T). It is not known from theprior art to use compaction techniques as specified above for thesubstantial reduction in pore volume according to the invention (that isto say to in excess of 70% TMD) of pulverulent mixtures or materialswhich serve as starting material for bodies made of hard metal.

[0052] An important field of application of bodies according to theinvention is punching tools.

[0053] Examples of gradual embodiments according to the invention areshown in FIGS. 1-4.

[0054] In the figures the differences in concentration of the componentsA and B are shown by grey tints. In this context white indicates arelatively low content of hard compound (a relatively large amount ofbinder) and black indicates a relatively large amount of hard compound(relatively little binder).

[0055] In FIG. 1 it can be seen that as a result of the very steepconcentration gradient in the compression surface after precompaction(midway between T and H) (some) transport of B still takes place duringHIP, which levels off the concentration gradient of B and a gradual hardmetal is spontaneously formed.

[0056] In FIGS. 2-4, in each of which a different sequence of A and B isused as the starting point, it can be seen that a shallow gradientyields too little driving force for diffusion of B, as a result of whichthe gradual composition is retained during HIP.

[0057] From the above examples it can thus clearly be seen that gradualpatterns of diverse types can be defined.

EXAMPLES

[0058] According to these examples hard metal is produced from a majorfraction of tungsten carbide and a minor fraction of cobalt. Thestarting materials used are the Grade 8 material known to those skilledin the art and WC/Co 70/30 with, respectively, 8 and 30% (m/m) Co. Inorder to make gradual hard metal these starting materials are mixed withone another in various ratios, as shown in the table below; see also the“stacking” in FIG. 5. TMD Grade WC/Co 70/30 Co fraction Hardness of endof mixture 8 fraction fraction in mixture product [GPa] [g/cm³] 100 0 81250 14.74 75 25 13.5 1120 14.18 50 50 19 1010 13.67 25 75 24.5 90013.19 0 100 30 810 12.74

[0059] The compositions (powder compacts) indicated in the above tableare precompacted to approximately 50% TMD by means of cold uniaxialpressing. This pre-pressing is carried out with the aid of a tube madeof stainless steel with an internal diameter of 20 mm and a wallthickness of 1.5 mm, which is closed off at one end by a stainless steelstopper (see also FIG. 5, which is discussed in more detail below). Thebottom half of the tube is then in each case filled with a hard metalpowder in the WC/Co mass ratio as indicated in the above table. The tophalf of the tube is filled with hard metal powder containing a Cofraction as indicated in the above table. After each introduction of asmall amount of powder the powder is subjected to uniaxial initialpressing under a pressure of approximately 100 MPa. After this fillingand precompaction process the tube is closed off at the top with astainless steel stopper.

[0060] An alternative embodiment of the precompaction of the powder isto make use of a cold isostatic press (CIP). In this case the powder (orthe various powder mixtures) are poured into a cylindrical rubbercontainer, after which the container is closed off by a stopper, that islikewise made of rubber. The container containing the powder is placedin the CIP filled with fluid, after which the CIP is hermeticallysealed. The fluid is brought up to pressure (3000 bar) using a pump, thepowder in the rubber container being isostatically precompacted. Aninitial density of the powder of 64% TMD is achieved by this method.After the cylindrical powder compact has been removed from the rubbercontainer a metal foil (copper foil with a thickness of 0.1 mm) iswrapped around it, by which means the diameter of the compact can bematched to the internal diameter of a metal tube that is just somewhatlarger. The tube is then closed off at both ends again using metalstoppers.

[0061] Dynamic compacti n

[0062] For the dynamic (explosive) compaction of the powder the tube isglued in place centred in a PVC cylinder having a length of 175 mm, aninternal diameter of 76 mm and a wall thickness of 4 mm. Theintermediate remaining space is filled with an explosive powder based onammonium nitrate. The detonation speed of the explosive powder is 3.6km/s. On detonation of the explosive (mainly) the diameter of the metaltube is reduced and by this means the hard metal powder is compacted toa relative density of approximately 90% TMD. A diagrammaticrepresentation of such a set-up for explosive compaction is shown inFIG. 5, in which the reference numerals have the following meaning:

[0063]1.=detonator;

[0064]2.=powder explosive;

[0065]3.=PVC tube;

[0066]4.=metal tube;

[0067]5.=hard metal powder;

[0068]6.=metal stopper;

[0069]7.=substrate.

1. Method for the production of a body made of hard metal, consisting ofa hard compound a and a binder b, wherein chosen amounts of pulverulenta and b, or of an optionally precompacted article that contains a and bin chosen amounts, are introduced into a container and the materialcontaining a and b is subjected to compaction in one or more steps inorder to increase the relative density (RD) to a value that is higherthan 70% of the theoretical maximum density (TMD) with the formation ofa body made of hard metal, in which on the one hand at least one zone(Za) containing a relatively large amount of B and, on the other hand,at least one zone (Zb) containing a relatively small amount of B arepresent and the amount of B gradually decreases from at least one zoneZa to at least one zone Zb, after which said body is optionallysubjected to sintering, hot isostatic pressing (HIP) or sinter HIP. 2.Method according to claim 1, wherein the material containing A and B iscompacted to a RD value in excess of 80% TMD, preferably in excess of90% TMD.
 3. Method according to claim 1 or 2, wherein the compaction iscarried out in two steps: (a) a first compaction (precompaction) toincrease the RD to a value of at most 70% TMD; (b) a second compactionin which the RD of the precompacted powder or article from step a) isfurther increased to a value above 70% TMD, preferably above 80% TMD, inparticular to above 90% TMD.
 4. Method according to one or more of thepreceding claims, wherein different mixtures of A and B are introducedinto two or more zones of the container, the mass ratios of A:B in thetwo or more zones having different values.
 5. Method according to one ormore of the preceding claims, wherein the container has an elongatedshape and the container is filled with different mixtures of A and B insuch a way that the quantity of binder at the one end of the shape (H)is lower than that at the other end of the shape (T).
 6. Methodaccording to one or more of the preceding claims, wherein the amount ofB in zone Zb is at least 1% (m/m) and the amount of B in zone Za is atmost 50% (m/m), the amounts being based on the mass of the totalmixture.
 7. Method according to one of the preceding claims, wherein theamount by mass of B, optionally gradually, increases from zone Zb tozone Za.
 8. Method according to one or more of the preceding claims,wherein A is chosen from the group consisting of diamond or carbidessuch as SiC, WC, TiC, TaC, NbC, ZrC, HfC, Cr₃C₂ and Mo₂C, nitrides suchas TiN, HfN and BN and borides such as TiB₂ and ZrB₂, preferablytungsten carbide, and wherein B is chosen from the group consisting ofthe metals Co, Cr, Ni, Fe (for example stainless steel) and alloysthereof, in particular cobalt.
 9. Method according to one or more of thepreceding claims, wherein the compaction is carried out at a temperatureat which no or virtually no mass transport of B or A takes place,preferably ambient temperature.
 10. Method according to one or more ofthe preceding claims, wherein use is made of static or (iso)dynamiccompaction techniques, preferably dynamic compaction techniques such aspneumomechanical uniaxial compaction; ballistic compaction; explosivecompaction, including shock compaction, and magnetic compaction, for thecompaction.
 11. Body obtainable according to the method of one or moreof the preceding claims.
 12. Body of hard metal comprising a hardcompound A and a binder B, the mass ratio of A:B changing over across-section of the body in order to impart to said body differentmechanical properties such as, on the one hand, toughness in at leastone zone Za or at at least one end (T) and, on the other hand, hardnessin at least one zone Zb or at at least one other end (H), the change inthe ratio of A:B being gradual.
 13. Body made of hard metal according toclaim 11 or 12, comprising a punching tool.
 14. Use of dynamiccompaction techniques as specified in claim 10 for the production ofone-piece bodies made of hard metal having at least one hard zone (Zb)or hard end (H) and at least one tough zone (Za) or tough end (T).